1. Field of the Invention
The present invention relates to an apparatus for forming a nano pattern; and, more particularly, to an apparatus for forming a nano pattern uniformly at a low cost and a method for forming the nano pattern using the same.
2. Description of the Related Art
Generally, a nano-patterning technique has been widely used in a semiconductor field such as circuit design, and so on, as a technique for forming a fine structure shape below 100 nm on a desired substrate.
In the nano-patterning technique, because patterns to be formed are very fine in comparison with the substrate on which the patterns are formed, a method for uniformly fabricating patterns with a desired shape on the wide substrate is becoming a key issue.
The nano-patterning technique is mainly divided into a nano imprinting method and a holographic lithography according to a principle of forming the patterns.
The nano imprinting method is a method of transferring a previously formed master shape to a substrate by using a mechanical principle similarly to a method of imprinting a stamp, wherein a pattern is formed by coating UV curable resin on a substrate, imprinting a master with a pattern thereon and curing the resin through UV rays. Therefore, the nano printing method has an advantage of obtaining the uniform shape on a region with the same size as the master only if the desired shape is formed on the master according to the principle of transferring the shape of the master to the substrate, and thus it is appropriate for mass-production of the same shape.
However, if a desired pattern is changed, the master should be newly fabricated to match with the changed pattern and further a fabrication cost of the master is very high, thereby deteriorating flexibility. Further, because the master should be periodically washed according to a characteristic of a process, the master should be replaced after producing a predetermined number of patterns, and equipment for nano imprinting is also very high, a process cost is greatly increased.
The holographic lithography is a method of transferring an interference pattern generated due to interference of a laser beam to a substrate by using an optical principle. This method has an advantage of improving flexibility by easily changing a period of the desired pattern through the controlling of an angle of a coherent beam without requiring the mask for forming the pattern. However, this method is not suitable for forming the uniform patterns over a wide area since a size of the beam is less than 1 mm according to a characteristic of a laser and a region on which the pattern is fabricated is very narrow. Hence, for fabricating the pattern over the wide area through the holographic lithography, two methods, i.e., a beam expansion method and a beam scanning method, are currently used.
The beam expansion method, one of the most widely used methods, is a method of producing a pattern by expanding a small laser beam to a predetermined size by using a lens and has an advantage of widening an area on which the pattern is produced by adding an optical unit for beam expansion in a general holographic lithography system. However, since this method merely expands the laser beam, it has a drawback that uniformity of the pattern is deteriorated as the pattern becomes more distant from a center of the beam according to a characteristic of the laser beam with Gaussian beam intensity distribution.
That is, while the beams pass through the beam expansion unit, diameters of the beams are increased so that the beams meet on a substrate to form an interference pattern, wherein the uniformity of the formed interference pattern tends to be reduced as the interference pattern gets away from a central part of the substrate according to the characteristic of the laser beam, and thus the pattern is hardly impressed on a position apart from the central part at a predetermined distance. Accordingly, to obtain the uniformity over a wide range, the beam should be expanded, but the intensity of the beam is reduced and an exposure time is extended, whereby the contrast of the interference pattern is deteriorated according to a characteristic of an interferometer which is sensitive to vibration and disturbance to prevent the pattern from being formed.
The beam scanning method is a method of fabricating a pattern over a wide area by scanning the entire surface of a substrate with a small laser beam and has an advantage of fabricating a very uniform pattern over the wide area, meanwhile, because many hours are required to perform the scanning over the wide area and a precise stage and a feedback system for scanning are needed to maintain an interference pattern during scanning, the beam scanning method is not economical.
That is, in case of the beam scan type, because a beam generated from the laser is directly used without installing an additional beam expansion unit, the formed pattern is very small and therefore in order to form the pattern on the entire surface of the substrate, the substrate is put on a stage for precisely controlling the substrate and scanned with the laser beam. Accordingly, the beam scan type has an advantage of forming the very uniform patterns on the entire surface of the substrate, but it has disadvantages of needing the very high cost precise stage and feedback control system for beam scanning and increasing a time of fabricating the pattern.